Hazrat Zaid bin Arqam (may Allah be pleased with him) says that once Hazrat Ali (may Allah be pleased with him) asked the people under oath, so sixteen companions (may Allah be pleased with them) stood up and testified that the Noble Prophet (peace and blessings be upon him) said: "Whoever loves me, Ali is also his beloved."
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 23143
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد ضعيف، أبو إسرائيل ليس بذاك القوي، وأبو سلمان مجهول